add hacky closure to struct_tail_with_normalize in order to allow us to walk valtrees in lockstep with the type

Author: b-naber

compiler/rustc_middle/src/ty/sty.rs

@@ -2273,7 +2273,7 @@ impl<'tcx> Ty<'tcx> {
         tcx: TyCtxt<'tcx>,
         normalize: impl FnMut(Ty<'tcx>) -> Ty<'tcx>,
     ) -> (Ty<'tcx>, bool) {
-        let tail = tcx.struct_tail_with_normalize(self, normalize);
+        let tail = tcx.struct_tail_with_normalize(self, normalize, || {});
         match tail.kind() {
             // Sized types
             ty::Infer(ty::IntVar(_) | ty::FloatVar(_))

compiler/rustc_middle/src/ty/util.rs

@@ -187,7 +187,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// if input `ty` is not a structure at all.
     pub fn struct_tail_without_normalization(self, ty: Ty<'tcx>) -> Ty<'tcx> {
         let tcx = self;
-        tcx.struct_tail_with_normalize(ty, |ty| ty)
+        tcx.struct_tail_with_normalize(ty, |ty| ty, || {})
     }
 
     /// Returns the deeply last field of nested structures, or the same type if
@@ -203,7 +203,7 @@ impl<'tcx> TyCtxt<'tcx> {
         param_env: ty::ParamEnv<'tcx>,
     ) -> Ty<'tcx> {
         let tcx = self;
-        tcx.struct_tail_with_normalize(ty, |ty| tcx.normalize_erasing_regions(param_env, ty))
+        tcx.struct_tail_with_normalize(ty, |ty| tcx.normalize_erasing_regions(param_env, ty), || {})
     }
 
     /// Returns the deeply last field of nested structures, or the same type if
@@ -220,6 +220,10 @@ impl<'tcx> TyCtxt<'tcx> {
         self,
         mut ty: Ty<'tcx>,
         mut normalize: impl FnMut(Ty<'tcx>) -> Ty<'tcx>,
+        // This is a hack that is currently used to allow us to walk a ValTree
+        // in lockstep with the type in order to get the ValTree branch that
+        // corresponds to an unsized field.
+        mut f: impl FnMut() -> (),
     ) -> Ty<'tcx> {
         let recursion_limit = self.recursion_limit();
         for iteration in 0.. {
@@ -235,12 +239,16 @@ impl<'tcx> TyCtxt<'tcx> {
                         break;
                     }
                     match def.non_enum_variant().fields.last() {
-                        Some(f) => ty = f.ty(self, substs),
+                        Some(field) => {
+                            f();
+                            ty = field.ty(self, substs);
+                        }
                         None => break,
                     }
                 }
 
                 ty::Tuple(tys) if let Some((&last_ty, _)) = tys.split_last() => {
+                    f();
                     ty = last_ty;
                 }
 

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1519,18 +1519,22 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
                 // Any type with multiple potential metadata types is therefore not eligible.
                 let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
 
-                let tail = selcx.tcx().struct_tail_with_normalize(self_ty, |ty| {
-                    // We throw away any obligations we get from this, since we normalize
-                    // and confirm these obligations once again during confirmation
-                    normalize_with_depth(
-                        selcx,
-                        obligation.param_env,
-                        obligation.cause.clone(),
-                        obligation.recursion_depth + 1,
-                        ty,
-                    )
-                    .value
-                });
+                let tail = selcx.tcx().struct_tail_with_normalize(
+                    self_ty,
+                    |ty| {
+                        // We throw away any obligations we get from this, since we normalize
+                        // and confirm these obligations once again during confirmation
+                        normalize_with_depth(
+                            selcx,
+                            obligation.param_env,
+                            obligation.cause.clone(),
+                            obligation.recursion_depth + 1,
+                            ty,
+                        )
+                        .value
+                    },
+                    || {},
+                );
 
                 match tail.kind() {
                     ty::Bool